Transducer pressure release system

ABSTRACT

A transducer pressure release system wherein the transducer element is supported between a radiating and a load mass, both of which are resiliently supported in a watertight housing. A pair of magnetic coacting coils, one of which is affixed to said housing and the other to one of the masses, are supplied current through a control means from a constant voltage source. The control means receives an input signal from a displacement sensor which detects the movement of one of the masses and fixes a current through the coils to restore the masses to a constant separation therebetween, thus providing isolation and proper pressure release.

ijnited States Patent [191 Schoen, Jr.

[ TRANSDUCER PRESSURE RELEASE SYSTEM [75] Inventor: Oscar W. Schoen,Jr., Ontario,

Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Oct. 29, 1969 21 Appl. No.: 872,433

3,349,367 10/1967 Wisotsky ..340/8X V0. 73466 LDNTROLLED VHF/051.6UR/ZENT 5o u/zcE Primary Examiner-Richard A. Farley Attorney, Agent, orFirm-Richard S. Sciascia; Arthur A. McGill [57] ABSTRACT A transducerpressure release system wherein the transducer element is supportedbetween a radiating and a load mass, both of which are resilientlysupported in a watertight housing. A pair of magnetic coacting coils,one of which is affixed to said housing and the other to one of themasses, are supplied current through a control means from a constantvoltage source. The control means receives an input signal from adisplacement sensor which detects the movement of one of the masses andfixes a current through the coils to restore the masses to a constantseparation therebetween, thus providing isolation and proper pressurerelease.

6 Claims, 2 Drawing Figures TRANSDUCER PRESSURE RELEASE SYSTEM Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to deep underwater transducer mounting andcompensation and more particularly pertains to a system of isolation andpressure release wherein a set of coacting electric coils are energizedand controlled by the movement of the face element of a transducerstructure to maintain a constant spacing of the masses abutting thetransducer and to pressure release a ceramic transducer without loss ofmechanoacoustic efficiency.

2. Description of the Prior Art In the field of electroacoustictransducers which are subjected to extreme static pressures, it has beenthe general practice to employ standard pressure release techniques tomaintain the efficiency of the transducer at great sea depths. In orderto overcome changes in ambient (static) pressure encountered, it hasbeen the practice to minimize the deflection of the radiating massrelative to the transducer element by providing pressure release or anelement which will compensate for the environmental hydrostaticpressure. Compressible pressure-relief elements inside the housing havebeen employed for this purpose. These have generally been of two types.One type is a gas medium such as air within the housing and in contactwith the radiating mass. The air or gas pressure is changed inaccordance with the ambient hydrostatic pressure to provide thenecessary stiffness. The other technique involves the use of solidmaterials, some of which contain air pockets or cells, such as foamrubber and plastics. Such techniques have been found unsatisfactory atgreat depths in that these conventional materials collapse under extremehydrostatic pressure and their pressure release capabilities aresubstantially reduced or eliminated entirely. Further, since thesematerials act as non-linear springs, a loss in compliance and anincrease in internal loss of the material occurs, as the vibrating massor element is increasingly coupled to the housing and results in amarked decrease in efficiency with an increase in the resonantfrequency.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a pressure release system for a deep submergence transducer thathas all the advantages of similarly employed prior art devices and hasnone of the above described disadvantages. To attain this, the presentinvention provides a unique transducer mass arrangement wherein thestress applied to the transducer by the environmental pressure on theradiating mass is compensated and serves as a pressure release. Therelative movement of the load mass is detected and the current through aset of opposing magnetic coils is controlled thereby to apply arestoring force to one of the transducer masses.

An object of the present invention is to provide a simple, inexpensive,direct and reliable pressure release arrangement for a deeply submergedtransducer.

Another object is to provide an automatic hydrostatic environmentalpressure compensation structural arrangement for underwater transducers.

A further object is to provide a self compensating efficient transducerwithout loss of compliance, increase in internal loss and decoupled fromthe housing.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a structural cross-sectionalview of a complete transducer embodiment made in accordance with theprinciple of this invention and employing a LVDT displacement element;and,

FIG. 2 is another embodiment made in accordance with this inventionshowing in cross-section the structural arrangement and in schematic thewiring arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the illustrated embodimentof FIG. 1, a watertight enclosure or housing 10 having an openend 11 isclosed thereacross by a radiating end mass 12. The end mass 12 issupported by a ring flange 13 to which it is circumferentially joined bya waterproof elastomeric adhesive 14 such as vulcanized rubber or epoxy.The opposite end of the ring flange 13 is bolted as at 15 to the housing10 with a waterproof ring gasket 16 therebetween. This form of mountingpermits limited movement of the radiating mass into and out of thehousing while it is in direct face contact with the surrounding externalliquid environment and resiliently supported by the housing. Supportedcentrally by the radiating mass is a cylindrical ceramic transducer 17(which may be of other forms). One such support, as illustrated, is bythreading one end 18 of the transducer in a mating threaded opening 19in the inner face of mass 12. Thus the transducer and the radiating massact relatively as a unitary vibrating structural element. As is standardpractice, the transducer has been polarized and provided with electrodedfaces across which the electrical signal may be applied, causing thetransducer to contract and elongate, which in turn vibrates the mass 12therewith. The above described details have been deleted from thedrawing, as well as the electrical connections thereto, for the sake ofsimplicity and clarity. Since the transducer will elongate it must beprovided with some means (backing) to hold one end thereof fixed topermit its motion to be applied to the mass 12. For this purpose anextremely large non-radiating backing end mass 20 is provided. Eventhough this nonradiating mass is made as large as practically possible,some motion will exist and must be isolated from the generated acousticoutput signal. The mass is cemented or affixed along its peripheral face21 to the housing by a pressure release material such as is the case ofthe radiating mass 12. Imperfections of these isolating techniques arisefrom the use of these materials placed between the transducer housingand the vibratingelement. As the external pressure is increased, thetransducer is forced to translate and bear against this isolationmaterial. Since this material acts as a non-linear spring, this resultsin a loss of compliance and an increase in internal loss of the materialand the vibrating element becomes increasingly mechanically coupled tothe housing.

The loading end mass is provided with a central cylindrical extension 22which extends into the hollow core of the transducer but is not incontact therewith. The end face 23 of the ceramic transducer tightlyabuts the end load mass 22. Carried by the opposite face 24 of the loadmass 20 for movement therewith is the core 25 and arm 26 of the linearvariable differential transformer (LVDT) 27. The transformer itself isan electro-mechanical transducer which produces a voltage outputdirectly proportional to the displacement of a movable armature ormagnetic core 25. The core is axially positioned inside threetransformer coils consisting of a primary 28 and two secondaries 29connected in series opposition which are encased and fixedly supportedby the rear housing wall 29 by structural support 30. When the primaryis energized with alternating current from an excitation source 32, avoltage output appears across the secondary circuit when the magneticcore is displaced from its central or null position. Suitable linearvariable differential transformers are presently available on thecommercial market. Such transformers are fully described in the datasheets of Columbia Research Laboratories, Inc. of Woodlyn, Pa. andavailable therefrom.

An annular recess 33 in the forward face 34 of load mass 20 carries asolenoidally wound coil 35 so as to provide an axially directed magneticfield when excited. Disposed forward of and in face to face relationwith said load mass is a coil support member 36 which is in a form sothat its outer edge surface 37 is rigidly fastened to the housing 10 andits central portion 38 deleted to permit the passage therethrough of thetransducer 17. This support member is also provided with an annularrecess 39 which is opposite and in registration with load mass recess 33and has therein a solenoid coil 40. The coils 35 and 40 are coupled andconnected to a variable current source 41 in a manner so that theirrespective generated magnetic fields coact to produce a force on theload mass 20 directed toward the radiating mass 12. This in effectforces the transducer in that direction (P,,,,,,,) so as to compensatefor the external hydrostatic pressure (P To this end, the displacementvoltage derived from the LVDT is applied to the control input of thesource 41 to control the current supplied to the two coacting coils andthereby hold the transducer in a fixed position irrespective of thehydrostatic pressure applied to the transducer without coupling to thehousing.

Consider now the embodiment shown in FIG. 2 wherein a portion of theentire structure is similar or identical to that disclosed in FIG. 1.The housing 100, the radiating mass 112 and its associated parts, theceramic transducer 117, as well as the load mass 120 are such similarcomponents. Here the displacement sensing means employed includes apiezoresistive transducer or pressure sensitive resistance element, someof which are fully described in the data sheets of Clark ElectronicLaboratories of Palm Springs Calif, and in the February 1963 issue ofInstruments and Control Systems on pages 93 and 94. Such materialsrespond to changes in applied pressure with large changes in electricalresistance and hence are referred to as pressure transducers. Affixedrigidly to the rear wall 124 of mass 120 is push rod 142 whose oppositeend terminates at one electrode 143, which with electrode 144 forms asandwich for the piezoresistive material 145. Electrode 144 is insulatedfrom the housing by a backing plate 146 which is supported'by thehousing rear wall 130. Annular support 136 fastened to the housing alongits peripheral edge is provided with an annular recess 139 and carriestherein solenoid coil 140. The coil support is disposed proximate theforward portion of the housing with the coil face directed rearwardly. Asecond coil support member 146 is carried by the radiating mass 112 onan annular arm 147 which is affixed thereto and the supported coil 148is in face to face relation with opposing coil 140. The electricalresistance of the piezoresistive material decreases when it iscompressed. One electrode 144 is connected to base 149 'of transistor150 while the other electrode 143 is connected via variable limitingresistor 151 to the emitter 152 of the transistor. The coils are tied inparallel with one end thereof connected to the collector 153 and withthe other end tied to one output terminal 154 of constant voltage supply155. This output terminal 154 is also connected to the base 149 throughfixed resistor 156. The other output terminal 157 is connected to oneterminal of the limiting resistor 151.

When the piezoresistive material is compressed by hydrostatic pressureon the radiating mass the resultant reduction in resistance causes amore positive voltage to appear at the base terminal 149 terminating inan increased current through the coils. This increase in coil currentincreases the magnetic force so as to increase the force P and offsetthe hydrostatic force P and thereby provide the necessary pressurerelease compensation therefor.

I claim:

1. An automatic pressure release system for an underwater transducerarrangement which comprises:

a waterproof housing having an opening at one end thereof,

a radiating mass resiliently mounted across said one end,

a load mass resiliently supported in said housing for movement towardand away from said radiating mass,

a transducer element supported between and in contact with said masses,

a pair of coacting magnetic field coils, one of said coilsrigidlyaffixed to said housing and the other of said coil coupled to oneof said masses,

a source of electrical energy for activating said coils,

a displacement sensing means coupled to said load mass for sensing thedisplacement thereof and providing an output dependent on saiddisplacement,

a control means connected to receive said sensing means output andcoupling therethrough said source and said coils for automaticallycontrolling the activation of said coils to maintain a constantseparation between said coils, independent of the hydrostatic pressureexternally applied to said radiating mass.

2. The pressure release system according to claim 1 wherein said sourceof electrical energy is a constant voltage source.

3. The pressure release system according to claim 1 wherein said controlmeans includes wherein 531d dlsplacemem Sensmg means 15 3 1111631 atransistor having a base, emitter and collector elevariable displacementtransformer.

4. The pressure release system according to claim 2 wherein saiddisplacement sensing means is a piezoresistive element.

ment, circuit means connecting the output of said piezoresistive elementbetween said base and said emitter,

5. The pressure release system according to claim 3 and wherein saidcontrol means is a voltage controlled varisecond cn'cult means Connectmg531d Source between able current source. said emitter and sald base.

6. The pressure release system according to claim 4

1. An automatic pressure release system for an underwater transducerarrangement which comprises: a waterproof housing having an opening atone end thereof, a radiating mass resiliently mounted across said oneend, a load mass resiliently supported in said housing for movementtoward and away from said radiating mass, a transducer element supportedbetween and in contact with said masses, a pair of coacting magneticfield coils, one of said coils rigidly affixed to said housing and theother of said coil coupled to one of said masses, a source of electricalenergy for activating said coils, a displacement sensing means coupledto said load mass for sensing the displacement thereof and providing anoutput dependent on said displacement, a control means connected toreceive said sensing means output and coupling therethrough said sourceand said coils for automatically controlling the activation of saidcoils to maintain a constant separation between said coils, independentof the hydrostatic pressure externally applied to said radiating mass.2. The pressure release system according to claim 1 wherein said sourceof electrical energy is a constant voltage source.
 3. The pressurerelease system according to claim 1 wherein said displacement sensingmeans is a linear variable displacement transformer.
 4. The pressurerelease system according to claim 2 wherein said displacement sensingmeans is a piezoresistive element.
 5. The pressure release systemaccording to claim 3 wherein said control means is a voltage controlledvariable current source.
 6. The pressure release system according toclaim 4 wherein said control means includes a transistor having a base,emitter and collector element, circuit means connecting the output ofsaid piezoresistive element between said base and said emitter, andsecond circuit means connecting said source between said emitter andsaid base.